Cob: baking in earthen walls?

[nigella1]

 Steve wrote:On the other hand, Texas, Oklahoma or whatever hot and humid
places are
different.  Some months it might not drop below 80 untill 2 am.  Not enough
cooltime  to dump your accumulated heat.   I do think that you could have a
baking problem with adobe or cob in hot humid climates.   Straw walls seem
most appropriate.  Metal roof.  cross ventilation, porches, high ceilings.
Shade.  All that.

Hi Steve,
 I have a few questions here, I live in hot humid Texas so this interests me
:)  First of all, I was curious as to why the high ceilings? Don't get me
wrong, I happen to love high ceilings .I would love to have a reason to
justify them . To me they make a house feel nicer.
 Secondly, aren't  there some cob building around Austin? Does any one know
how well they perform as to keeping cool? I've been to Austin a couple of
times, seems like it was hot and humid there , too.
 Lastly, I was curious about the metal roofing. It is used a lot around here
but I have always wondered if it would serve to heat a house in summer? I
have to admit total ignorance on this point. My experience is limited to
wrapping a potatoe in foil and popping it in the oven...
nigella